This project proposes an examination of the basis of multi-vesicular granule (MVG) formation by HIV-1 nef. In cells expressing SIV and HIV nef, CD4 is endocytosed and rapidly degraded. The P.I. has demonstrated that nef expression induces MVG formation and these granules are morphologically similar to those found in cytolytic cells where they serve both endocytic and secretary/biosynthetic functions. The investigator suggests that the MVG compartment in nef expressing cells may function similarly and may facilitate processing of newly synthesized proteins. In the first specific aim the investigator will characterize the multi- vesicular compartment in CD4+ T lymphocytes and will evaluate the biogenesis, composition and function of these granules in nef-expressing cells. The investigator will determine whether these nef-induced granules facilitate envelope glycoprotein processing and determine whether it is CD4-dependent. Through subcellular fractionation techniques the investigator will determine whether granules present in nef expressing cells contain CD4, nef and envelope glycoproteins in order to determine whether they localize to this compartment. In the second specific aim the investigator will mutagenize nef to determine regions important for CD4 downregulation and granule formation. With this information, the investigator will identify regions of nef that are important for its in vitro effects.